Various attempts for suppressing longitudinal streaks from occurring in images have been conventionally made in a developing device having a developing roller and a thickness regulating blade for regulating the thickness of a toner layer carried on the developing roller.
For example, JP-A-10-063095 discloses such a technique relating to a developing device that a rigid material is used as a surface of a developing roller, and an elastic foamed material is used as a toner regulating blade, whereby surface flaws on the developing roller are prevented from occurring to suppress image deterioration, such as longitudinal streaks, from occurring.